Abstract

Space weather including solar activity and background plasma sets up spacecraft conditions that can magnify the threat from hypervelocity impacts. Hypervelocity impactors include both meteoroids, traveling between 11 and 72 km/s, and orbital debris, with typical impact speeds of 10 km/s. When an impactor encounters a spacecraft, its kinetic energy is converted over a very short timescale into energy of vaporization and ionization, resulting in a small, dense plasma. This plasma can produce radio frequency (RF) emission, causing electrical anomalies within the spacecraft. In order to study this phenomenon, we conducted ground-based experiments to study hypervelocity impactplasmas using a Van de Graaff dust accelerator. Iron projectiles ranging from 10−16 g to 10−11 g were fired at speeds of up to 70 km/s into a variety of target materials under a range of surface charging conditions representative of space weather effects. Impactplasmas associated with bare metal targets as well as spacecraft materials were studied. Plasma expansion models were developed to determine the composition and temperature of the impactplasma, shedding light on the plasma dynamics that can lead to spacecraft electrical anomalies. The dependence of these plasma properties on target material, impact speed, and surface charge was analyzed. Our work includes three major results. First, the initial temperature of the impactplasma is at least an order of magnitude lower than previously reported, providing conditions more favorable for sustained RF emission. Second, the composition of impactplasmas from glass targets, unlike that of impactplasmas from tungsten, has low dependence on impact speed, indicating a charge production mechanism that is significant down to orbital debris speeds. Finally, negative ion formation has a strong dependence on target material. These new results can inform the design and operation of spacecraft in order to mitigate future impact-related space weather anomalies and failures.

Received 05 October 2012Accepted 13 February 2013Published online 04 March 2013

Acknowledgments:

This study was sponsored by Los Alamos National Laboratory. The authors thank P. Colestock, S. Green, and the personnel of the Cosmic Dust Group at MPIK for their support during the experiments, J. Likar for the contribution of sample spacecraft materials, and J. Doolittle and G. King for their assistance in our plasma sensor calibration.